It is actually possible that you have a VoLte supported phone but you are not able to use it because you haven't enabled it yet.
- Following is the universal method to enable Volte for all android phone:
- Dial *#*#4636#*#*
- Select Volte Provisioned flag under Phone Information
- Restart your phone.
The other simple way includes enabling from call setting:
- Open Dialer app.
- Click on three dots for Settings.
- Go in Sim & Network.
- Look for Volte option.
- Enable the radio button
- You are good to go.
You can see detailed specs here: Realme C2